The Role of Dense Slurry in Achieving Zero Liquid Discharge

Abstract

The Coal Combustion Residual (CCR) and Effluent Limitations Guidelines(ELGs) rules pose significant technical and economic challenges for ash management and for treatment and discharge of flue gas desulfurization (FGD) wastewater at coal-fired power plants. Beneficial use is always a priority for ash, but only about half is being reused on a national basis, and the rest is destined for disposal. The U.S. Environmental Protection Agency identified biological treatment as the baseline treatment technology for FGD wastewater in the ELGs. However, it is becoming evident that bioreactors exhibit high capital and operating costs, occupy significant space, and are sensitive to changes in temperature and pH. Dense slurry ash management can sequester large quantities of FGD wastewater along with the contained contaminants through hydration, encapsulation, and entrainment for a fraction of the cost of traditional treatment. By using dense slurry sequestration of FGD wastewater, off-site discharge of effluent can be avoided altogether. Dense slurry was employed at (among other plants) the Matra Power Plant near Budapest, Hungary, and this technology played a key role in helping the plant achieve zero liquid discharge (ZLD). The Matra project is summarized and data are presented that show how the technology helped the plant achieve ZLD and other environmental objectives.